1. Field of Use
This invention relates generally to modulatable power transmission clutches and, in particular, to those wherein a fluid-applied spring-released piston operates on clutch plates disposed between a rotatable driving member and a rotatable driven member to effect clutch modulation.
2. Description of the Prior Art
U.S. Patent application Ser. No. 643,357, filed Dec. 22, 1975 to Schneider et al for "Swing Control for Crane", now U.S. Pat. No. 4,070,926, and assigned to the same assignee as the present application discloses a power transmission system for swinging the upper section of a mobile crane in opposite directions. That power transmission system employs a transmission having a pair of alternately actuatable "wet" type prior art transmission clutches therein. Each transmission clutch includes a rotatable driving member, a rotatable driven member, and slippingly engagable clutch plates between said members. Each clutch is modulatable between a minimum engaged position and a fully engaged position by means of application of pressurized hydraulic fluid from an operator-controlled proportional solenoid valve to a fluid-applied spring-released movable piston which is embodied in the clutch and acts upon the clutch plates. Such a clutch is modulatable by applying fluid at various pressures to the piston and is able, for example, with a clutch plate diameter of about 9 inches, to transmit dynamic torques in the range of 4500 to 8000 ft. lbs. and hold static torques equal to or up to 150% of that value. Such a clutch is designed so as to have enough friction material area in its clutch plates so as not to create thermal problems within the clutch and cause distress or failure.